Variable inductor



Aug. 20, 1929. R L DAVIS 1,725,060

VARIABLE INDUCTOR Filed Sept. 7, 1926 Y fwlTNEssEsz- 475.4%

l 7 ATrRNEY Patented Aug. 20, 1929.

.UNITED STATES- PATENT OFFICE..

ROBERT L. DAVIS, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC MANUFACTURING COMPANY, A CORPORATION 0F PENNSYLVANIA.

VARIABLE INDUCTOR.

Application filed September' 7, 1926. Serial No. 133,811.

My invention relates to variable inductors, and it has particular relation to variable inductors adapted to be utilized as antenna loading coils.

One of the provide a variable inductor that will be selfsupporting.

Another object of my invention is to provide an inductor that is capable of `continuous variation.

Still another and more specific object of my invention is to provide an antenna loading coil that 'is Capable of being easilyand quickly installed and which has constants that are not sensibly varied by changing weather conditions. The antennaloadingcoils employed in the past have, in general, been constructed by winding a sniiicient number of turns of conducting material upon a plurality of insulating supports. Inasmuch as these coils are usually exposed to the weather, when in use, it is obvious that-rain or snow will, to a certain extent, affect the insulation between the several turns. It has also-been the custom with' such loading coils to vary the inductance thereof by means of movable clips attached to a flexible conductor, the clips being attached to suitable portions of the exterior of the coil.

In moving the clips from one position to another on the coil, the iexible leads therefrom tend to partially encircle the vcoil per se, adding to or subtracting from the effective inductance thereof, depending u on the direction in which the clip is move Under such circumstances, an accurate pre-de- '.termination of the inductance is practically impossible.

By my invention, I have entirely obviated the necessity of using a iexible lead to the movable, inductance-varying clip, substituting .therefor a rigid rod. I further contemplate the use of rigid wire or tubing for the loading coil itself, supporting the coil4 only from the opposite ends thereof.

The novel features which I believe'to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and its method of operation,

objects of my invention is to will best be understood by reference to the following description, taken in connection with the accompanying drawings.

Fig. 1 is a side elevational view of a preferred embodiment of my invention.

Fig.A 2 is an end elevational view of the same.

Fig. 3 is a detail view of an alternative form o vf Contact device.

Referring specifically to Figs. 1 and 2, a helix 1, constructed of wire or tubing sufficiently strong to bc self-supporting, is maintained in position by having the ends 2y and 3 thereof clamped to insulating supports 4 and 'by means of clamping devices 6 andl 7. An extension y8 of the insulating support 5 carries an adjustable clamping device 9 through which passes a rigid conductor 11. The conductor 11 projects into the interior cf thehelix 1 and, at its inner end,.it terminates in a bent portion 12, on the extreme end of which is a device 13 adapted to make Contact with the inner sur face of the helix 1.

The rigid conductor 11 is rotatable and slidable in the clamping device 9, permitting the contact device 13 to be positioned at any point on the helix.

Vhen it is desired to change the effective inductance of the helix, the clamping device 9 is loosened, permitting the rigid conductor 11 to, move freely therein. By a proper manipulation of the conductor 11, the end contact element 13 may be moved along the helix to a predetermined position, it being obvious that, as the Contact element rotates about the axis of the helix, the rigid'conductoigwill pass longitudinally through the clamping device.

Under certain conditions, it may be desirable to permanently fix the position of the contact element 13 on ythe helix, and, for this purpose, a contact element of the type illustrated in Fig. 3 may be employed. The bent .portion 12 of the rigid conductor 11 mayterminate in a clamping device 14 comprising a fixed` element 15 attached to the conductor and a movable element 16, the. two being held together by an adjusting screw 17. Each of these elements is provided with a channel, the two channels defining a space (itl 'lil

18 to receive thevhelix 1. 'By loosening the adjusting screw 17, the two portions of the clamping device may be separated sufiiciently to permit movement of the helix therethrough. the finally determined position being maintained by a tightening of the screw.

The Contact device, in addition toits pri- 'mary function, has the additional functionv of supplying added support to the helix. rlliis .additional support is of importance when the helix attains a considerable length.

lt is believed to be apparent ,to those skilled in the art that my invention is not confined to antenna loading coils but that it may equally as Well be applied to solenoids of the type ordinarily used as loosecouplers, or to the tuning coils customarily employed in radio receiving and -transmitting sets.

The principal advantage attending the use of my invention results from the fact that the inductance of a helix may be changed Without involving the uncertainty introduced by the customary flexible lead. The rigid conductor of my invention maintains a ixed axial relation to the helix, and the variation in length of the conductor has a negligible effect on the total' inductance. ln addition, it will be noted that the Contact element may be movedl aroundthe entire inner circumference of 4the helix Without disconnecting and replacing the same, as is the case when the customary movable clip is applied to the outer surface of the helix. The likelihood of leakage from the flexible conductor to adjacent portions of the apparatus is avoided, such leakage being a matter of importance when highpotentials and frequencies are employed.

While I have shown but one rspeciiic embodiment of my invention, it is not my intention to be limited thereby. My invention is accordingly not to be limited except in so far as is necessitated by the prior art and by the spirit of the appendedclaims.

I claim as my invention: l

1. An inductance device and a three-point support therefor, one of said supports being positioned in the interior of said device and being movable axially thereof.

2. A spirally-wound inductance device, supports to which the ends of said nductance device are secured, a conductor located axially within said inductance. device, means b which said conductor may make contact Wit i the inductance device, and clamping means and means carried by said conductor for Inaking electrical contact with the interior of said inductor.

5. A variable inductance device and a plu-l rality of supports therefor, one of said supports Yconstituting the variation means, and means carried by said'la'st named support for securing it in adjustable relation inductance device.

6. In combination, a plurality of insulating supports, an inductor carried therebetween, a clamp carried by one of said supports, a conducting member held by said clamp and positioned Within said inductor, and means carried by said conducting member for making electrical contact with the interior of said inductor, said last named means being'capable of securing said conducting member to said inductor at any desired point thereon.

In testimony whereof, I have hereunto subscribed 1926.

ROBERT L. DAVIS.

to said my name this iirst day 0f September, 95 

